Method for casting metals with melting points greater than 200° celsius using a plastic mold which mold conforms to the shape of the object to be cast used in conjunction with rapid cooling

ABSTRACT

This present disclosure relates to a method for casting metals with melting points greater than 200° Celsius using a Plastic Mold which mold conforms to the shape of the object to be cast used in conjunction with Rapid Cooling.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the priority filing benefit of U.S. Provisional Patent application No. 62/990,300 filed Mar. 16 2020 and U.S. Provisional Patent application No. 63/053,639 filed Jul. 19 2020, incorporated herein by reference in its entirety.

BACKGROUND

Casting is a process in which a molten metal is delivered into a mold that contains a hollow cavity which duplicates the intended shape of the object to be produced. The molten metal is introduced into the mold whereupon the metal is allowed to cool and solidify. The metal casting is then extracted from the mold.

Molds currently used in casting metal are created from materials with a melting point equal to or higher than the molten metal in order to reduce or eliminate the mold from melting due to the heat of the molten metal. Some of these mold materials may include sand, fine silica slurry, steel, and graphite.

Sand is the most versatile and commonly used casting material. It is the principle component of sand casting and has a very high melting temperature allowing its use with many types of metals. Removing the metal casting requires the casting to cool over an extended period of time whereupon the sand mold must be destroyed to remove the casting and a new mold must be prepared for another casting. This casting removal and mold preparation is an expensive, time consuming, and labor intensive process.

Fine silica slurry is the principle component in a casting process called investment casting. Investment casting, like sand casting, allows the casting of many types of metals due to the molds high melting temperature. This process may be even more expensive and labor intensive than sand casting due to the many steps required to make a single mold.

Steel is often used to create metal molds. Steel molds are commonly used in the casting of metals such as zinc, aluminum, copper, and steel. A steel mold is very expensive to create and may only be used for a limited number of castings because of the wearing of the mold due such things as metal erosion, heat deformation, and part extraction.

Graphite is sometimes used to create cast metal molds. Graphite is more commonly used for low temperature metals such as zinc. Nonetheless graphite molds for production are time consuming to use, expensive to prepare, and wear quickly.

There exist a great need for an effective, economical, and versatile means to cast metals with a melting point greater than 200° Celsius which means is now fulfilled in this disclosure.

There is no discovered relevant prior art relating to the use of a method for casting metals with melting points greater than 200° Celsius using a Plastic Mold which mold conforms to the shape of the object to be cast used in conjunction with Rapid Cooling.

Prior art, U.S. Pat. No. 7,125,512 B2 (Crump et al.) discloses a method for making a prototype plastic injection molded part. This Crump application does not disclose a method for casting metals with melting points greater than 200° Celsius using a Plastic Mold which mold conforms to the shape of the object to be cast. This Crump application also does not disclose the use of Rapid Cooling.

Prior art US 2016/0067766 A1 (Verreault et al.) discloses the use of a 3d printed mold for casting amorphous alloys using molds of metal or ceramic. As quoted in the Verreault application, “with one embodiment, the mold is printed using a metal. In accordance with another embodiment, the mold is printed using a ceramic.” The Verreault application also discloses the specific use of these molds for “casting of amorphous alloys.” The Verreault patent does not disclose the use of a method for casting metals with melting points greater than 200° Celsius using a Plastic Mold which mold conforms to the shape of the object to be cast. The Verreault application does not disclose the use of a mold for casting non-amorphous alloys.

Prior art US 2016/0325493 A1 (DeSimone et al.) discloses an “Immersive 3D Continuous Printing of Casting Molds For Metals and other Materials”, wherein the mold is constructed by “providing a carrier and a build plate, said build plate comprising a semipermeable member, said semipermeable member comprising a build surface with said build Surface and said carrier defining a build region there between, and with said build surface in fluid communication by way of the semipermeable member with a source of polymerization inhibitor;”. This method of mold construction as described within the DeSimone application is not required nor disclosed within the current application. This DeSimone application also does not disclose the use of Rapid Cooling.

Prior art US 2016/0346831 A1 (Snyder et al.) discloses the use of an additively manufactured wax mold used to create a wax model which in turn is used to create a casting mold for use in investment casting. “FIG. 1 illustrates a wax mold 20 used to form a wax model 22 (see FIG. 2), that in turn is used to generally form a casting mold 24 (see FIG. 3) for the manufacture of a workpiece”.

This Snyder application does not disclose the use of a Plastic Mold conforming to the shape of the object to be cast for casting metals with melting points greater than 200°. This Snyder application also does not disclose the use of Rapid Cooling.

Prior art US 2019/0077054 A1 (Jessen et al.) discloses the use of a device for the manufacturing of a mold which device requires “a container for providing at least one mould material, a build platform having a build surface for holding and/or supporting at least one mould being or having been manufactured by an additive manufacturing process, a source for providing energy to selectively activate, and if required subsequently solidify, the at least one mould material in or from the container to enable additive manufacturing of the mould, and an electronic controller” none of which is disclosed or required in the current application. This Jessen application does not disclose the use of a Plastic Mold conforming to the shape of the object to be cast for casting metals with melting points greater than 200°. This Jessen application also does not disclose the use of Rapid Cooling.

None of the prior arts disclosed the use of a method for casting metals with melting points greater than 200° Celsius using a Plastic Mold which mold conforms to the shape of the object to be cast used in conjunction with Rapid Cooling.

FIELD

This present disclosure relates to a method for casting metals with melting points greater than 200° Celsius using a Plastic Mold which mold conforms to the shape of the object to be cast wherein the Plastic Mold has an interior surface conforming to the shape of the object to be cast and incorporating means whereby molten metal may be introduced into the cavity created by said interior surface, and an exterior surface set at such offset from the interior surface so as to create a wall typically between 1 to 10 millimeters thick thereby creating a thin wall mold, which Plastic Mold is to be used in conjunction with Rapid Cooling wherein this Rapid Cooling is the use of a cooling fluid introduced to the exterior surface so that the heat from the molten metal transfers through the wall of the Plastic Mold to the cooling fluid at a sufficient rate and duration so to allow the Plastic Mold to maintain its integrity for a sufficient duration so that the molten metal begins the solidification process.

Object of this Embodiment

It is therefore an object of this present disclosure to disclose a method for casting metals with melting points greater than 200° Celsius using a Plastic

Mold which mold conforms to the shape of the object to be cast wherein the Plastic Mold has an interior surface conforming to the shape of the object to be cast and incorporating means whereby molten metal may be introduced into the cavity created by said interior surface, and an exterior surface set at such offset from the interior surface so as to create a wall typically between 1 to 10 millimeters thick thereby creating a thin wall mold, which Plastic Mold is to be used in conjunction with Rapid Cooling wherein this Rapid Cooling is the use of a cooling fluid introduced to the exterior surface so that the heat from the molten metal transfers through the wall of the Plastic Mold to the cooling fluid at a sufficient rate and duration so to allow the Plastic Mold to maintain its intergrity for a sufficient duration so that the molten metal begins the solidification process.

SUMMARY

This present disclosure discloses the use of a Plastic Mold conforming to the shape of the object to be cast used in conjunction with Rapid Cooling to effect casting metals with a melting temperature higher than 200° Celsius.

The features of this present disclosure are set forth with particularity in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top plan view of an embodiment of the present disclosure;

FIG. 2 is a section view taken along line A-A of FIG. 1;

FIG. 3 is a front isometric view of FIG. 1 taken along line A-A of FIG. 1;

FIG. 4 is a top plan view of an embodiment of the present disclosure;

FIG. 5 is a section view taken along line B-B of FIG. 4;

FIG. 6 is a front isometric view of FIG. 4 taken along line B-B of FIG. 4;

FIG. 7 is a representation of a finished cast product using the process herein described in this patent disclosure;

FIG. 8 is a depiction of a cross section view of a casting of the present disclosure wherein the Plastic Mold has not lost its integrity;

FIG. 9 is a depiction of a cross section view of a casting of the present disclosure should the Plastic Mold loose its integrity;

These figures use the following numeric designations.

-   An embodiment of the present disclosure 10. -   An embodiment of the present disclosure 20. -   Mold Cavity 30. -   Mold exterior surface 32 -   Inner mold wall surface 34 -   Mold wall 36 -   Mold molten metal inlet 38 -   Plastic Mold 40 -   Optional mold outlet 50 -   Rapid Cooling Fluid 65 -   Rapid Cooling Fluid Conduit 70 -   A representation of a finished casting using the process herein     described in this patent disclosure 100 -   Chill zone of the casting 110 -   Columnar zone of the casting 120 -   Equiaxed zone of the casting 130 -   Mold wall with lost integrity 140

DETAILED DESCRIPTION OF THIS EMBODIMENT

FIG. 1 shows a top plan view of an embodiment 10 of the present disclosure consisting of the Plastic Mold 40 which mold conforms to the shape of the object to be cast incorporating at least one outer mold wall surface 32 and at least one inner mold wall surface 34 wherein inner mold wall surface 34 encompasses the Mold Cavity 30. Molten metal may be directly introduced into Mold Cavity 30 through Mold molten metal inlet 38 allowing the introduction of molten metal into Mold Cavity 30 from without Mold Cavity 30. Optional mold outlet 50 facilitates the flow of metal and air from within Mold Cavity 30 to without Mold Cavity 30. As further illustrated by FIG. 1, there exist Rapid Cooling Fluid Conduit 70 which directs the flow of a Rapid Cooling Fluid 65 onto the outer mold wall surface 32. In this embodiment Rapid Cooling Fluid Conduit 70 is separate and distinct entity from Plastic Mold 40.

FIG. 2 is a section view along line A-A of the embodiment depicted by FIG. 1.

FIG. 3 is a front isometric view along line A-A of the embodiment depicted by FIG. 1.

As depicted in FIG. 1, FIG. 2, and FIG. 3, Rapid Cooling Fluid Conduit 70 may exist separate from the mold.

FIG. 4 shows a top plan view of an embodiment 20 of the present disclosure consisting of the Plastic Mold 40 incorporating at least one outer mold wall surface 32 and at least one inner mold wall surface 34 wherein inner mold wall surface 34 encompasses the Mold Cavity 30. Molten metal may be directly introduced into Mold Cavity 30 through Mold molten metal inlet 38 allowing the introduction of molten metal into Mold Cavity 30 from without Mold Cavity 30. Additionally there exist Rapid Cooling Fluid Conduit 70 which directs the flow of a Rapid Cooling Fluid 65 onto maintaining the integrity of the casting by rapidly cooling mold.

FIG. 5 is a section view along line B-B of the embodiment depicted by FIG. 4.

FIG. 6 is a front isometric view along line B-B of the embodiment depicted by FIG. 4.

As depicted in FIG. 4, FIG. 5, and FIG. 6, Rapid Cooling Fluid Conduit 70 may exist integral with the mold.

FIG. 7 is a representation of a casting 100 using the process herein described in this patent disclosure.

FIG. 8 is a depiction of a cross section view of a casting 100 of the present disclosure wherein the Plastic Mold has not yet lost its integrity.

FIG. 9 is a depiction of a cross section view of a casting 100 of the present disclosure should the Plastic Mold have lost its integrity after the solidification of the outer skin of the object to be cast.

Other configurations of the present disclosure are also possible and within the scope of the embodiment of the present disclosure, such as the Plastic Mold 40 being constructed of more than one piece in the manner of molds typically used in die casting and injection molding.

The representations given within this patent disclosure illustrate the most anticipated uses of this embodiment although not to the exclusion of any other embodiment or method.

OPERATION OF THE PRESENT DISCLOSURE

This patent discloses a mold which conforms to the shape of the object to be cast wherein the herein disclosed Plastic Mold reduces the time, effort, and expense of manufacture over more traditional molds while allowing the casting of metals with melting points greater than 200° Celsius through the use of Rapid Cooling. Plastic Molds may also allow highly complex castings to be manufactured which castings may not be possible with conventional casting techniques.

Plastics generally fall within two categories, General Use and High Performance. General use plastics include but are not limited to thermoplastics such as polylactic acid (PLA), Acrylonitrile butadiene styrene (ABS), Polyethylene terephthalate and its derivatives such as PET, PETG, PETT, Nylon and its derivatives, thermoplastic elastomers (TPE) such as Thermoplastic polyurethane (TPU) and Thermoplastic copolyester (TPC) and thermoset plastics such as 3D systems Pro-Blk, Somos® 9120, Somos® 9420, and Design Concept Modeling resin.

High Performance plastics include but are not limited to thermoplastics such as PolyEtherEtherKetone (PEEK) and its derivatives, PolyEtherKetoneKetone (PEKK) and its derivatives, Polyphenylsulfone (PPSF or PPSU) and its derivatives, Polysulfone (PU) and its derivatives, polycarbonate (PC) and its derivatives, ULTEMTM 9085 and blends thereof, ULTEMTM 1010 and blends thereof, and thermoset plastics such as 3D Systems Hi Temp 300, Formlabs FLHTAM01, Peopoly Moai Hi-Temp Nex Resin, Somos® Taurus, and Somos® PerFORM.

The general criteria in this patent disclosure for determining what constitutes general use plastics is either an extrusion temperature less than 260° C. for thermoplastics or heat deflection temperature less than 98° C. at 66 psi for thermoset plastics.

The general criteria in this patent disclosure for determining what constitutes high performance plastics is either an extrusion temperature equal to or greater than 260° C. for thermoplastics or heat deflection temperature equal to or greater than 98° C. at 66 psi for thermoset plastics.

The development of additional thermoplastic and thermoset compounds are anticipated and within the scope of this patent disclosure such as the addition of metals and metal alloys, ceramics, etc. within the plastic to assist or modify the characteristics of the plastic to alter the properties of the mold, the properties of the casting, the appearance of the castings, etc. Such additional elements included in the plastic are within the scope of this patent disclosure.

When used conjointly with Rapid Cooling, both general use and high performance plastics can be used to create shape conforming molds for metals including but not limited to zinc, aluminum, copper, brass, bronze, stainless steel, mild steel, etc. and their various alloys and compounds. As a rule of thumb, general use plastics are used for the molds for casting zinc and aluminum and their various alloys and compounds, and high performance plastics for the casting of copper, brass, bronze, stainless steel, mild steel, etc. and their various alloys and compounds. This rule does not exclude the possibility of general use plastics used in the casting of copper, brass, bronze, stainless steel, mild steel, etc. and their various alloys and compounds, nor does it exclude the use of high performance plastics for the casting of zinc and aluminum and their various alloys and compounds.

It is important to note that the methods of producing the Plastic Mold are well known and understood, which methods may include but are not limited to:

Injection Molding,

Resin Infusion Molding,

Transfer Molding,

Compression Molding,

Reaction Injection Molding,

Extrusion Molding,

Rotational Molding,

Vacuum Molding

Matched Molding,

Trapped-sheet Contact-Heat Pressure Forming,

Low Pressure Molding,

Vacuum Plug Assist Molding,

Pressure Assist Plug Molding,

Lost Foam Casting,

Twin-Sheet Forming,

Selective Laser Sintering,

Fused Deposition Modeling,

Fused Filament Modeling,

Stereolithography,

Digital Light Processing,

Material Jetting

Drop On Demand,

Binder Jetting,

And all other methods for molding/shaping plastic currently in use or used in the future. These other methods are within the scope of this disclosure.

This patent disclosure also discloses the method of using these Plastic Molds to cast molten metals with a melting point above 200° C. using the process of Rapid Cooling. Rapid Cooling is the application of a fluid at a temperature lower than that of the molten metal such that the fluid removes heat through the wall of the Plastic Mold at a sufficient rate such that the metal in the mold forms a solid “skin” such that this solid skin is durable enough to retain the shape of the casting should the Plastic Mold loses its integrity thereby maintaining the form of the casting even if the mold has deformed or disintegrated. It is imperative this Rapid Cooling is initiated prior to, during, or immediately after the introduction of the molten metal into the Plastic Mold so as to promote the formation of the aforementioned solid skin should the Plastic Mold loses its integrity. The length of time to initiate Rapid Cooling is usually between 6 seconds prior to 8.0 seconds after the molten metal has been introduced into the Mold Cavity, although other lengths of time are anticipated and within the scope of this patent disclosure.

The ‘skin’ of solid metal which forms during the cooling of the molten metal is call the ‘chill zone’ as shown by numeral 110 in FIGS. 8 and 9. This chill zone can vary in depth from microns to millimeters depending on the metal cast, the plastic used for the mold, how much heat is removed, and how quickly the heat is removed. If a large amount of heat is removed quickly, it is common for the casting to have a larger chill zone whereas if the heat is removed more slowly it is common to have a smaller chill zone. Here is where the nucleation phase of the solidification process takes place which results in a layer of relatively uniform metal crystal formation. As more heat is removed the columnar zone is formed wherein the metal grains grow towards the center of the casting in long thin columns that are perpendicular to the casting surface. Finally the center of the casting, the equiaxed zone, contains spherical, randomly oriented crystals.

This Rapid Cooling in conjunction with a Plastic Mold which mold conforms to the shape of the object to be cast wherein the Plastic Mold has an interior surface conforming to the shape of the object to be cast and incorporating means whereby molten metal may be introduced into the cavity created by said interior surface, and an exterior surface set at such offset from the interior surface so as to create a wall typically between 1 to 10 millimeters thick thereby creating a thin wall mold, which combination of thin wall mold and rapid cooling this said mold thereby allowing the casting of metals with a melting point greater than 200° Celsius into the aforementioned Plastic Mold, is the main object of the present disclosure.

It is important to note that the Plastic Mold may be constructed of one unified structure such as is commonly employed in investment casting, or constructed of multiple pieces such as is commonly employed in injection molding. It is recognized that the Plastic Mold may needs be created in more than one piece due to the limitations of the means of mold creation. For example, if the means of mold creation is a 3d printer, the build plate of the 3d printer may not be of sufficient size to create the entire mold in one operation thereby requiring the mold to be created in multiple pieces through multiple operations. If the means of mold creation is an injection press, then there will exist a limitation on the size of the item due to the limitations of the injection press.

Should the mold be created in multiple operations, there will be the need to unite the mold into one piece. This may require uniting the mold through the use of methods such as, but not limited to, chemical bonding, heat bonding, or physical joining. Such means of bonding is well understood and within the scope of the present application. Physically joining multiple pieces of a mold may also be desirable so as to aid in the extraction of the finished part from within the mold. Such means and methods for physically joining multiple pieces of a mold so as to aid in the extraction of the finished part from within the mold are well understood and within the scope of the present application.

It is important to note that the configuration and operation of the Rapid Cooling Fluid Conduit may be integral or independent of the Plastic Mold. For example, integrating the Rapid Cooling Fluid Conduit may facilitate the delivery of Rapid Cooling Fluid to otherwise difficult to administer areas of the mold while having the Rapid Cooling Fluid Conduit independent of the mold may be preferable for larger molds requiring greater quantities of Rapid Cooling Fluid for adequate cooling.

Thusly the use of Rapid Cooling for cooling a plastic mold for casting metals with melting points greater than 200° Celsius using a Plastic Mold which conforms to the shape of the object to be cast is disclosed in this patent disclosure. The examples of methods for achieving Rapid Cooling disclosed are only representations of methods of Rapid Cooling. Multitudes of various methods for Rapid Cooling are anticipated and within the scope of this patent disclosure.

The operation of the present disclosure is thus. A molten metal is introduced into Mold Cavity 30 through Mold molten metal inlet 38 whereupon the heat transfers from within the Mold Cavity 30 through inner mold wall surface 34, continuing through mold wall 36 and through outer mold wall 32 into the Rapid Cooling Fluid 65 which has been delivered to outer mold wall 32 by means of Rapid Cooling Fluid Conduit 70, whereupon Rapid Cooling Fluid 65 is replaced and replenished by additional Rapid Cooling Fluid 65 in order to continue the process of heat extraction thereby maintaining the integrity of the casting 100.

Traditionally the molten metal would gradually cool and harden within the mold but this process would deform the Plastic Mold before the metal casting has cooled sufficiently to retain its shape.

The present application discloses the method of Rapid Cooling so to promote and maintain the integrity of the casting by rapidly cooling mold exterior surface 32 such that the heat transferred through mold wall 36 and inner mold wall surface 34 is of such duration and magnitude so as to create a chill zone 110 of sufficient integrity so that the metal molded object 100 maintains its shape even if the Plastic Mold loses its integrity.

The Rapid Cooling Fluid 65 may be comprised of many well-known and understood substances such as but not limited to water, water ice, Ethyl Alcohol, Isopropyl Alcohol, Ethylene Glycol, Propylene Glycol, Glycerol, Fluorinated Hydrocarbons, air, carbon dioxide, dry ice, nitrogen, argon, etc. Other cooling fluids are also anticipated and included in the present disclosure. Plastic Mold 40 as depicted in FIGS. 1 through 3, and 4 through 6, illustrate, but not in a limiting sense, the wide spectrum of potential mold designs available for use. Plastic Mold 40 as depicted in FIGS. 1 through 3 discloses filling of the mold with molten metal by gravity feed through Mold molten metal inlet 38 with air and metal exiting through Optional mold outlet 50, whereas Plastic Mold 40 as depicted in FIGS. 4 through 6 discloses filling of the mold through Mold molten metal inlet 38 with the molten metal being forced up through the mold and not requiring Optional mold outlet 50.

It is noted that Rapid Cooling Fluid Conduit 70 may be any means whereby the Rapid Cooling Fluid may be delivered to Plastic Mold 40. There exist different methods of delivering Rapid Cooling Fluid 65 through Rapid Cooling Fluid Conduit 70 to the Plastic Mold 40 Mold exterior surface 32 including but not limited to spraying, injection, fans, immersion, or other such methods. Such methods are common and well understood and within the scope of the invention.

It is important to recall and within the scope of this patent application that Plastic Mold 40 may be a unified structure such as is commonly employed in investment casting, or constructed of multiple pieces such as is commonly employed in injection molding.

It is also noted and within the scope of this patent application that Plastic

Mold 40 may utilize additional pieces made of metal or other materials in order to facilitate the functioning of the mold. For example it may be required for Plastic Mold 40 to have adapters made of metal, plastic, ceramic, or other such material so to adapt Plastic Mold 40 and Rapid Cooling Fluid Conduit 70 to systems which facilitate the introduction of the molten metal from without Plastic Mold 40 to within Plastic Mold 40, to facilitate the removal of air and metal from within Plastic Mold 40 to a location outside Plastic Mold 40, or the introduction and removal of Rapid Cooling Fluid 65. It is also envisioned that additional pieces made of metal or other materials may be required to secure or otherwise support Plastic Mold 40 as a unified structure or multiple pieces to a system which facilitates or enables the process of metal introduction to Plastic Mold 40 and the application of Rapid Cooling Fluid 65.

Thereby this process of using a mold which conforms to the shape of the object to be cast in conjunction with Rapid Cooling may create metal molded parts using metals with melting points greater than 200° Celsius. 

1. A method comprising: a mold constructed of plastic which mold incorporates at least one outer mold wall surface and at least one inner mold wall surface wherein inner mold wall surface encompasses a mold cavity;
 2. The method of claim 1, wherein there exist an inlet to the mold cavity allowing the introduction of molten metal into the mold cavity from without the mold;
 3. The method of claim 2, wherein there exist a conduit which directs the flow of a cooling fluid onto the outer mold wall surface thereby facilitating the removal of the heat of the molten metal from within the mold cavity into the cooling fluid, thereby cooling the metal within the mold cavity;
 4. The method of claim 3, wherein there may exist a mold outlet which facilitates the flow of metal and air from within the mold cavity to without the mold.
 5. A method comprising: forming a plastic mold for receipt of a molten metal with a melting point greater than 200° Celsius;
 6. The method of claim 5, wherein the plastic mold comprises a hollow interior between inner and outer walls, and wherein the hollow interior is configured to receive the metal for molding the molten metal between the inner and outer walls;
 7. The method of claim 6, further comprising a channel for communicating molten metal from without the plastic mold to said hollow interior;
 8. The method of claim 7, further comprising a channel for communication of a fluid to the outer walls of the plastic mold for the purpose of cooling the plastic mold.
 9. A method comprising: a mold for the casting of metals with melting points greater than 200° Celsius comprising; a mold constructed of plastic which mold incorporates at least one outer mold wall surface and at least one inner mold wall surface wherein inner mold wall surface encompasses a mold cavity; an inlet to the mold cavity allowing the introduction of molten metal into the mold cavity from without the mold cavity; a conduit which directs the flow of a cooling fluid onto the outer mold wall surface thereby facilitating the removal of heat from the molten metal within the mold cavity through the inner mold wall surface proceeding through the outer mold wall surface into the cooling fluid, thereby cooling the metal within the mold cavity;
 10. The mold of claim 9, wherein there may exist a mold conduit or conduits which facilitates the flow of metal and air from within the mold cavity to without the mold cavity. 